1. Field of the Invention
This invention relates to a straightening unit for cast strand in a continuous casting machine, and, more particularly, to a Z-shape strand withdrawal/straightening unit which, in a bow type or vertical type continuous casting machine, a Z-shape strand with a unsymmetric cross section having a different roll contact surface height at each side on the top surface is unbent and drawn by press rolls.
2. Description of the Related Art
In a bow type continuous casting machine or a vertical bending type continuous casting machine, a cast strand exiting from a mold being solidified is drawn downward in strand guide by a series of pinch rollers, unbent to a horizontal state at a straightening unit near the exit by a press roller, and cut into a predetermined length to be made a bloom or beam blank as the final cast steel strand. A plurality of press roller stands for straightening a cast steel strand while drawing are positioned at a straightening unit, and, at the beginning of casting, a dummy bar is drawn by the pressure and rotation of these press rollers. Then, the initial cast strand guided in a curved state following the dummy bar is pressed down and drawn while unbending to a straight state.
Conventionally, many cast steel strand such as beam blanks, blooms, or slabs produced by such continuous casting machine have a rectangular cross section with flat and parallel top and bottom surfaces. Alternatively, a beam blank may have the deformed cross section as shown in FIG. 1. Even in this case, top roller contact surfaces 1c, 1d are formed at the same height in respect to bottom roll contact surfaces 1a, 1b. It is unbent and drawn by a press roller with a flat rolling surface. Therefore, a dummy bar 2 supporting the beam blank 1 and providing the drawing force for it (FIG. 2) is also pressed and drawn on its roller contact surfaces 2a, 2b, 2c, and 2d by the same press roller. However, a Z-cast strand as shown in FIG. 3 has different heights H.sub.1, H.sub.2 on the top roller contact surfaces 3b, 3c in respect to a bottom roller contact surface 3a. Therefore, the top press roller must be a roller with a different diameter as shown in FIG. 6. In this case, a dummy bar 2 with a flat top and bottom roller contact surfaces cannot be pressed and drawn. Thus, such Z-cast strand have not been manufactured by a conventional continuous casting process.